On a night of very still air, stars twinkle less than usual.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a night of very still air, stars twinkle less than usual. Why? And why does Jupiter shine steadily even on a windy night?
Need a reminder? The key ideaShow
The air is denser near the ground, so starlight bends as it comes down. Stars look higher, and they twinkle as the air moves. The Sun is seen about before true sunrise and after true sunset.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Still air. Twinkling comes from layers of air that move and keep changing the bending. With still air, the bending hardly changes, so the starlight flickers less.
Step 2. Jupiter. A planet is close enough to be a tiny disc, many points of light together. Their flickers do not keep in step, so they cancel, and the total light stays steady.
Answer: less moving air means less change in the bending; a planet's many points average out.
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